The Chaco War (1932–1935) (Spanish: Guerra del Chaco, Guarani: Cháko Ñorairõ[9]) was fought between Bolivia and Paraguay over control of the northern part of the Gran Chaco region (known in Spanish as Chaco Boreal) of South America, which was thought to be rich in oil. It is also referred to as La Guerra de la Sed (Spanish for "The War of the Thirst") in literary circles, for being fought in the semi-arid Chaco. It was the bloodiest military conflict fought in South America during the 20th century, between two of its poorest countries, both having previously lost territory to neighbors in 19th century wars.

During the war, both landlocked countries faced difficulties shipping arms and supplies through neighboring countries. Bolivia faced particular external trade problems, coupled with poor internal communications. Although Bolivia had lucrative mining income, and a larger better equipped army, a series of factors turned the tide, and Paraguay came to control most of the disputed zone by war's end.

The ultimate peace treaties granted two-thirds of the disputed territories to Paraguay.

The origin of the war is commonly attributed to a conflict between the oil companies Royal Dutch Shell backing Paraguay and Standard Oil supporting Bolivia.[10] The discovery of oil in the Andean foothills sparked speculation that the Chaco might be a rich source of petroleum, and foreign oil companies were involved in the exploration. Standard Oil was already producing oil from wells in the high hills of eastern Bolivia, around Villa Montes.[10] Scholar Rafael Archondo disputes claims that the war would have been caused by interests of these companies and emphasizes the aims of Argentina to import oil from the Chaco.[10]

In international arbitration, Bolivia argued that the region had been part of the original Spanish colonial province of Moxos and Chiquitos to which Bolivia was heir. Meanwhile, Paraguay based its case on the occupation of the land. Indeed, both Paraguayan and Argentine planters were already breeding cattle and exploiting quebracho woods in the area,[13] while the small nomadic indigenous population of Guaraní-speaking tribes was related to that country's own Guaraní heritage. As of 1919, Argentine banks owned 400,000 hectares of land in the eastern Chaco, while the Casado family, a powerful member of the Argentine oligarchy, held 141,000.[14] The presence of Mennonite colonies in the Chaco, who settled there in the 1920s under the auspices of the Paraguayan Parliament, was another factor in favour of Paraguay's claim.[15]

The first confrontation between the two countries dates back to 1885, when the Bolivian entrepreneur Miguel Araña Suárez founded Puerto Pacheco, a port on the upper Paraguay river, south of Bahía Negra. He assumed that the new settlement was well inside Bolivian territory, but Bahía Negra had been implicitly recognized as Paraguayan by Bolivia. The Paraguayan government sent in a naval detachment aboard the gunboat Pirapó, which forcibly evicted the Bolivians from the area in 1888.[16][17] The incident was followed by two agreements -in 1894 and 1907– which were never approved by either the Bolivian or the Paraguayan parliament.[18] Meanwhile, in 1905, Bolivia founded two new outposts in the Chaco, Ballivián and Guachalla, this time along the Pilcomayo River. The Bolivian government ignored the half-hearted Paraguayan official protest.[17]

Bolivian penetration in the region went unopposed until 1927, when the first blood was shed over the Chaco Boreal. On 27 February a Paraguayan army patrol and its native guides were taken prisoners near the Pilcomayo River and held in the Bolivian outpost of Fortin Sorpresa, where the commander of the Paraguayan platoon, Lt. Adolfo Rojas Silva, was shot and killed in suspicious circumstances. Fortín (Spanish for "little fort") was the name used for the small pillbox and trench-like garrisons in the Chaco, although the troops' barracks usually were no more than a few mud huts. While the Bolivian government formally regretted the death of Rojas Silva, the Paraguayan public opinion called it "murder".[14] After the subsequent talks arranged in Buenos Aires failed to produce any agreement and eventually collapsed in January 1928, the dispute grew violent. On 5 December 1928 Fortin Vanguardia, an advance outpost established by the Bolivian army a few miles northwest of Bahía Negra, was overrun by a Paraguayan cavalry unit, which captured 21 Bolivian soldiers and burnt the scattered huts to the ground.[19] The Bolivians retaliated with an air strike on Bahía Negra on 15 December, which didn't cause many casualties or much damage. On 14 December Fortin Boquerón, which later would be the site of the first major battle of the campaign, was seized by Bolivia at the cost of 15 Paraguayan dead. A return to the status quo ante was eventually agreed on 12 September 1929 in Washington, under the pressure of the Pan American League, but an arms race had already begun and both countries were on a collision course.[20]

The 146km-long railway from the Paraguay river to the heart of the Chaco was vital for the Paraguayan army, especially during the battle of Boquerón

Paraguay had a population only a third as large as that of Bolivia (880,000 vs. 2,150,000), but its guerrilla style of fighting, compared to Bolivia's more conventional strategy, enabled it to take the upper hand. In June 1932 the Paraguayan army totaled about 4,026 men (355 combat officers, 146 surgeons and non-combatant officers, 200 cadets, 690 NCOs and 2,653 soldiers). Both racially and culturally, the Paraguayan army was practically homogeneous. Almost all of its soldiers were European-Guaraní mestizos. Bolivia's army, however, consisted mostly of Altiplano's aboriginals of Quechua or Aymará descent (90% of the infantry troops), the lower-ranking officers were of Spanish or other European ancestry, and army commander-in-chief Hans Kundt was German. In spite of the fact that the Bolivian army had more manpower, it never mobilized more than 60,000 men, and never more than two-thirds of the army were on the Chaco at any one time. Paraguay, on the other hand, mobilized its entire army.[21] Paraguay's war effort was a total one. Buses were commandeered to transport troops, wedding rings were donated to buy weapons, and by 1935 Paraguay had widened conscription to include 17-year-olds and policemen.

While both armies deployed a significant number of cavalry regiments, these actually served as infantry, since it was soon learned that the Chaco could not provide enough water and forage for horses. Only a relatively few mounted squadrons carried out reconnaissance missions at divisional level.[22] In the course of the conflict, Paraguayan factories developed their own type of hand grenade, the carumbe'i (Guaraní for "little turtle")[23][24] and produced trailers, artillery grenades and aerial bombs. The Paraguayan war effort was centralized and led by the state-owned national dockyards, managed by José Bozzano.[25][26] The Paraguayan army received the first consignment of carumbe'i grenades in January 1933.[23]

The Paraguayans took advantage of their ability to communicate over the radio in Guaraní, a language not spoken by the average Bolivian soldier. Paraguay had little trouble in transporting its army in large barges and gunboats on the Paraguay River to Puerto Casado, and from there directly to the front lines by railway, while the majority of Bolivian troops had to come from the western highlands, some 800 km away and with little or no logistic support. In fact, it took a Bolivian soldier about 14 days to traverse the distance, while a Paraguayan soldier only took about four.[21] The heavy equipment used by Bolivia's army made things even worse. The water supply in the dry climate of the region played a key role during the conflict. There were thousands of non-combat casualties due to dehydration, mostly among Bolivian troops.

One of the key Paraguayan assets was the gunboat Humaitá, shown here shortly after being laid down in Italy, without her main armament.

The Chaco War is also important historically as the first instance of large-scale aerial warfare to take place in the Americas. Both sides used obsolete single-engined biplane fighter-bombers; the Paraguayans deployed 14 Potez 25s, while the Bolivians made extensive use of at least 20 CW-14 Ospreys. Despite an international arms embargo imposed by the League of Nations, Bolivia in particular went to great lengths in trying to import a small number of Curtiss T-32 Condor II twin-engined bombers disguised as civil transport planes, but they were stopped in Peru before they could be delivered.[27]

The Paraguayan navy played a key role in the conflict by carrying thousands of troops and tons of supplies to the front lines via the Paraguay River, as well as by providing anti-aircraft support to transport ships and port facilities.[28]

Two Italian-built gunboats, the Humaitá and Paraguay ferried troops to Puerto Casado. On 22 December 1932 three Bolivian Vickers Vespas attacked the Paraguayan riverine outpost of Bahía Negra, on the Paraguay River, killing an army colonel, but one of the aircraft was shot down by the gunboat Tacuary. The two surviving Vespas met another gunboat, the Humaitá, while flying downriver. Paraguayan sources claim that one of them was damaged.[29][30] Conversely, the Bolivian army reported that the Humaitá limped back to Asunción seriously damaged.[31] Although the Paraguayan navy admitted that Humaitá was struck by machine gun fire from the aircraft, they claimed that her armour shield averted damage.[32]

Shortly before 29 March 1933 a Bolivian Osprey was shot down over the Paraguay River,[33] while on 27 April a strike force of six Ospreys launched a successful mission from their base at Muñoz against the logistic riverine base and town of Puerto Casado, although the strong diplomatic reaction of Argentina prevented any further strategic attacks on targets along the Paraguay River.[34] On 26 November 1934, the Brazilian steamer Paraguay was strafed and bombed by mistake by Bolivian aircraft while sailing the Paraguay River near Puerto Mihanovich. The Brazilian government sent 11 naval planes to the area, and its navy begun to convoy shipping on the river.[35][36][37]

The Paraguayan navy air service was also very active in the conflict, harassing Bolivian troops deployed along the northern front with flying boats. The aircraft were moored at Bahía Negra Naval Air Base, and consisted of two Macchi M.18s.[38] These seaplanes carried out the first night air attack in South America when they raided the Bolivian outposts of Vitriones and San Juan,[39] on 22 December 1934. Every year since then, the Paraguayan navy celebrates the "day of the Naval Air Service" on the anniversary of the action.[40]

The Bolivian army deployed at least ten locally-built patrol boats and transport vessels during the conflict,[41] mostly to ship military supplies to the northern Chaco through the Mamoré-Madeira system.[42] The transport ships Presidente Saavedra and Presidente Siles steamed on the Paraguay River from 1927 until the beginning of the war, when both units were sold to private companies.[41] The 50-ton armed launch Tahuamanu, based in the Mamoré-Madeira fluvial system, was briefly transferred to Laguna Cáceres to ferry troops downriver from Puerto Suárez, challenging for eight months the Paraguayan naval presence in Bahía Negra. She was withdrawn to the Itenez River in northern Bolivia after Bolivian aerial reconnaissance revealed the actual strength of the Paraguayan navy in the area.[41][43]

On June 15, 1932, a Bolivian detachment captured and burned to the ground the Fortín Carlos Antonio López at Pitiantutá Lake, disobeying explicit orders by Bolivian President Daniel Salamanca to avoid provocations in the Chaco region. One month later, on July 16, a Paraguayan detachment evicted the Bolivian troops from the area. The lake was at 21°19′38″S59°44′12″W﻿ / ﻿21.32722°S 59.73667°W﻿ / -21.32722; -59.73667 and had been discovered by Paraguayan explorers in March 1931, but the Bolivian High Command was unaware of this when one of its aircraft spotted the lake on April 1932.

After the initial incident, Salamanca changed his status quo policy over the disputed area and ordered the outposts of Corrales, Toledo and Boquerón to be captured. The three were soon taken, and in response Paraguay called for a Bolivian withdrawal. Salamanca instead demanded that they be included in a "zone of dispute". On a memorandum directed to President Salamanca on August 30, Bolivian Gen. Filiberto Osorio expressed his concerns over the lack of a plan of operations, and attached a plan of operations focusing on an offensive from the north. At the same time Bolivian Gen. Quintanilla asked for permission to capture two additional Paraguayan garrisons—Nanawa and Rojas Silva. During August Bolivia slowly reinforced its 4,000-men-strong First Bolivian Army, located in the zone of conflict, with 6,000 men.

The breaking of the fragile status quo in the disputed areas of the Chaco by Bolivia convinced Paraguay that a diplomatic solution on agreeable terms was not possible. Paraguay gave its general staff orders to recapture the three forts. During August Paraguay mobilized over 10,000 troops and sent them into the Chaco region. Paraguayan Lieutenant Colonel José Félix Estigarribia prepared for a large offensive before the Bolivians would have mobilized their whole army.

Fortín Boquerón was the first target of the Paraguayan offensive. The Boquerón complex, guarded by 619 Bolivian troops, resisted a 22-day siege by a 5,000-man Paraguayan force. An additional 2,500 Bolivians attempted to relieve the siege from the southwest but were beaten back by 2,200 Paraguayans who defended the accesses to the siege area. A few Bolivian units managed to enter Fortín Boquerón with supplies and the Bolivian Air Force dropped food and ammunition to the besieged soldiers. Having begun on 9 September, the siege ended when Fortín Boquerón finally fell on 29 September 1932.

After the fall of Fortín Boquerón, the Paraguayans continued their offensive and executed a pincer movement, which forced parts of the Bolivian force to surrender. While the Paraguayans had expected to lay a new siege on Fortín Arce, the most advanced Bolivian outpost in the Chaco, when they got there they found it in ruins. The 4,000 Bolivians who defended Arce had retreated to Fortín Alihuatá and then to Saavedra[disambiguation needed].

In December 1932 Bolivian war mobilization had concluded. In terms of weaponry and manpower, its army was ready to virtually overpower the Paraguayans. Gen. Hans Kundt, a former German officer who was a veteran of fighting on the Eastern Front in World War I, was called by President Salamanca to lead the Bolivian counteroffensive. Kundt had intermittently sojourned in Bolivia since the beginning of the century, establishing good relationships with members of the Bolivian political elite. Before the First World War he had been in the service of the Bolivian army as a trainer and counselor, and thus enjoyed great prestige in Bolivia for having, to some extent, shaped the Bolivian army, and also for his services in the army of the German Empire.

Vickers 6-ton similar to those deployed by the Bolivian army in the Chaco War

The Paraguayan Fortín Nanawa was chosen as the main target of the Bolivian offensive, to be followed by the command centre at Isla Poí. Their capture would allow Bolivia to reach the Paraguay River, putting the Paraguayan city of Concepción in danger. The capture of the fortines of Corrales, Toledo and Fernández by the Bolivian Second Corps were also part of Kundt's offensive plan.

In January 1933 the Bolivian First Corps began its attack on Fortín Nanawa. This stronghold was considered by the Paraguayans to be the backbone of their defenses. It had zig-zag trenches, miles of barbed wire and many machine-gun nests (some embedded in tree trunks). The Bolivian troops had previously stormed the nearby Paraguayan outpost of Mariscal López, isolating Nanawa from the south. On January 20, 1933, Kundt, in personal command of the Bolivian force, launched six to nine aircraft and 6,000 unhorsed cavalry, supported by 12 Vickers machine guns. However, the Bolivians failed to capture the fort and instead formed a defensive amphitheater in front of it. The Second Corps managed to capture Fortín Corrales and Fortín Platanillos but failed to take Fortín Fernández and Fortín Toledo. After a siege that lasted from February 26-March 11, 1933, the Second Corps aborted its attack on Fortín Toledo and withdrew to a defensive line built 15 km from Fortín Corrales.

Paraguayan troops in Fortin Alihuatá, 1932

After the ill-fated attack on Nanawa and the failures at Fernández and Toledo, Kundt ordered an assault on Fortín Alihuatá. The attack on this fortín overwhelmed its few defenders. The capture of Alihuatá allowed the Bolivians to cut the supply route of the Paraguayan First Division. When the Bolivians were informed of the isolation of the First Division, they launched an attack on it. This attack led to the Battle of Campo Jordán, which concluded in the retreat of the Paraguayan First Division to Gondra.

In July 1933 Kundt, still focusing on capturing Nanawa, launched a massive frontal attack on the fortín, in what came to be known as the Second Battle of Nanawa. Kundt had prepared for the second attack in detail, using artillery, airplanes, tanks and flamethrowers to overcome Paraguayan fortifications. The Paraguayans, however, had improved existing fortifications and built new ones since the first battle of Nanawa. While the Bolivian two-pronged attack managed to capture parts of the defensive complex, these were soon retaken by Paraguayan counterattacks made by reserves. The Bolivians lost more than 2,000 men injured and killed in the second battle of Nanawa, while Paraguay lost only 559 men injured and dead. The failure to capture Nanawa and the heavy loss of life led President Salamanca to criticize the Bolivian high command, ordering them to spare more men. The defeat seriously damaged Kundt's prestige. In September he resigned his position as commander in chief, but his resignation was not accepted by the president. Nanawa was a major turning point in the war, because the Paraguayan army regained the strategic initiative that had belonged to the Bolivians since the beginning of 1933.[44]

In September Paraguay began a new offensive in the form of three separate encirclement movements in the Alihuatá area, which was chosen because Bolivian forces there had been weakened by the transfer of soldiers to attack Fortín Gondra. As a result of the encirclement campaign, the Bolivian regiments Loa and Ballivián, totaling 509 men, surrendered. The Junín regiment suffered the same fate, but the Chacaltaya regiment was able to escape encirclement due to intervention of two other Bolivian regiments.

The success of the Paraguayan army led Paraguayan President Eusebio Ayala to travel to the Chaco to promote José Félix Estigarribia to the rank of general. In that meeting the president approved Estigarribia's new offensive plan. On the other side, the Bolivians gave up their initial plan of reaching the Paraguayan capital of Asunción and moved on to defensive and attrition warfare.

The Paraguayan army executed a large-scale pincer movement against Fortín Alihuatá, repeating the previous success of these operations. Seven thousand Bolivian troops had to evacuate Fortín Alihuatá. On December 10, 1933, the Paraguayans finished the encirclement of the 9th and 4th divisions of the Bolivian army. After unsuccessful attempts to break through Paraguayan lines and having suffered 2,600 dead, 7,500 Bolivian soldiers surrendered. Only 900 Bolivian troops managed to slip away. The Paraguayans obtained 8,000 rifles, 536 machine guns, 25 mortars, two tanks and 20 artillery pieces from the captured Bolivians. The remaining Bolivian troops withdrew to their headquarters at Muñoz, which was set on fire and evacuated on 18 December. Gen. Kundt resigned as chief of staff of the Bolivian army.

The massive defeat at Campo de Vía forced the Bolivian troops near Fortín Nanawa to withdraw northwest to form a new defensive line. Paraguayan Col. Rafael Franco proposed to launch a new attack against Ballivián and Villa Montes, but was turned down, as Paraguayan President Eusebio Ayala thought Paraguay had already won the war. A 20-day ceasefire was agreed upon between the warring parties on December 19, 1933. On January 6, 1934, when the armistice expired, Bolivia had reorganized its eroded army, having assembled a larger force than the one involved in its first offensive.

By the beginning of 1934 Paraguayan Gen. Estigarribia was planning an offensive against the Bolivian garrison at Puerto Suárez, 145 km upriver from Bahía Negra. The Pantanal marshes and the lack of canoes to navigate through them convinced the Paraguayan commander to drop the idea and turn his attention to the main front.[45] After the armistice's end the Paraguayan army continued its advance, capturing the outposts of Platanillos, Loa, Esteros, Jayucubás. After the battle of Campo de Vía in December the Bolivian army built up a defensive line at Magariños-La China. The Magariños-La China line was carefully built and considered to be one of the finest defensive lines of the Chaco War. However, a small Paraguayan attack on February 11, 1934, managed to breach the line, to the surprise of the Paraguayan command, forcing the abandonment of the whole defensive line. A Paraguayan offensive towards Cañada Tarija managed to surround and neutralize 1,000 Bolivian troops on March 27.

In May 1934 the Paraguayans detected a gap in the Bolivian defenses that would allow them to isolate the Bolivian stronghold of Ballivián and force its surrender. The Paraguayans worked at night to open a new route in the forests to make the attack possible. When Bolivian reconnaissance aircraft noticed this new path being opened in the forest, a plan was set up to let the Paraguayans enter halfway up the path and then attack them from the rear. The Bolivian operation resulted in the Battle of Cañada Strongest between May 18 and 25. The Bolivians managed to capture 67 Paraguayan officials and 1,389 soldiers. After their defeat at Cañada Strongest the Paraguayans continued their attempt to capture Ballivián. It was considered a key stronghold by the Bolivians, mostly for its symbolic position as the most southeastern Bolivian position left after the Second Paraguayan Offensive.

In November 1934 Paraguayan forces once again managed to surround and neutralize two Bolivian division, at El Carmen. This disaster forced the Bolivians to abandon Ballivián and form a new defensive line at Villa Montes. On November 27, 1934, Bolivian generals confronted President Salamanca while he was visiting their headquarters in Villa Montes and forced him to resign, replacing him with the Vice President, José Luis Tejada. On November 9, 1934, the 12,000-man-strong Bolivian Cavalry Corps managed to capture Yrendagüé and put the Paraguayan army on the run. Yrendagüé was one of the few places with fresh water in that part of the Chaco and, while the Bolivian cavalry was marching towards La Faye from Yrendagüé, a Paraguayan force captured all the wells in Yrendague so that upon their return the exhausted and thirsty Bolivian troops found themselves without water; the already weakened force fell apart. Many were taken prisoner and a great number of those who avoided capture died of thirst and exposure after wandering aimlessly through the hot, dry forest. The Bolivian Cavalry Corps had previously been considered one of the best units of the new army formed after the armistice.

Paraguayan offensive, January 1935. In blue, the Paraguayan advances, and in red, the Bolivian counterattacks

After the collapse of the northern and northeastern fronts, Bolivian defenses focused on the south to avoid the fall of their war headquarters/supply base at Villa Montes. The Paraguayans launched an attack towards Ybybobó, isolating a portion of the Bolivian forces on the Pilcomayo River. The battle began on 28 December 1934 and lasted until the early days of January 1935. The result was that 200 Bolivian troops were killed and 1,200 surrendered, with the Paraguayans losing only a few dozen men. Some fleeing Bolivian soldiers were reported to have jumped into the fast-flowing waters of the Pilcomayo River to avoid capture.

After this defeat the Bolivian army prepared for a last stand at Villa Montes. The loss of that base would allow the Paraguayans to reach the proper Andes. Col. Bernardino Bilbao Rioja and Col. Oscar Moscoso were left in charge of the defenses, after other high-ranking officers declined. On 11 January 1935 the Paraguayans encircled and forced the retreat of two Bolivian regiments. The Paraguayans also managed in January to cut off the road between Villa Montes and Santa Cruz.

Paraguayan commander-in-chief Gen. José Félix Estigarribia decided then to launch a final assault on Villa Montes. On 7 February 1935 some 5,000 Paraguayans attacked the heavily fortified Bolivian lines near Villa Montes, with the aim of capturing the oilfields at Nancarainza, but they were beaten back by the Bolivian First Cavalry Division. The Paraguayans lost 350 men and were forced to withdraw north toward Boyuibé. Estigarribia claimed that the defeat was largely due to the mountainous terrain, conditions in which his forces were not used to fighting.[46] On 6 March, Estigarribia again focused all his efforts on the Bolivian oilfields, this time at Camiri, 130 km north of Villa Montes. The commander of the Paraguayan 3rd Corps, Gen. Franco, found a gap between the Bolivian 1st and 18th Infantry regiments and ordered his troops to attack through it, but they became stuck in a salient with no hope of further progress. The Bolivian Sixth Cavalry forced the hasty retreat of Franco's troops in order to avoid being cut off. The Paraguayans lost 84 troops taken prisoner and more than 500 dead were left behind. The Bolivians lost almost 200 men, although—unlike their exhausted enemies—they could afford a long battle of attrition.[47] On 15 April the Paraguayans punched through the Bolivian lines on the Parapetí River, taking over the city of Charagua. The Bolivian command launched a counter-offensive that forced the Paraguayans back. Although the Bolivian plan fell short of its target of encircling an entire enemy division, they managed to take 475 prisoners on 25 April. On 4 June 1935 a Bolivian regiment was defeated and forced to surrender at Ingavi, in the northern front, after a last attempt at reaching the Paraguay River.[48] On 12 June, the day the ceasefire agreement was signed, Paraguayan troops were entrenched only 15 km from the Bolivian oil fields in Cordillera Province.

While the military conflict ended with a comprehensive Paraguayan victory,[49][50] from a wider point of view it was a disaster for both sides. Bolivia's Criollo elite forcibly impressed large numbers of the male indigenous population into the army, even though they felt little or no connection to the nation-state, while Paraguay was able to foment nationalist fervor among its predominantly mixed population. On both sides—but more so in the case of Bolivia—soldiers were ill-prepared for the dearth of water and the harsh conditions of terrain and weather they encountered. The effects of the lower-altitude climate had seriously impaired the effectiveness of the Bolivian army: most of its indigenous soldiers lived on the cold Altiplano at altitudes of over 12,000 feet (3,700 m). They found themselves at a physical disadvantage when called upon to fight in tropical conditions at almost sea level.[51] In fact, of the war's 100,000 casualties—about 57,000 of them Bolivian—more died from diseases such as malaria and other infections than from combat-related causes. At the same time, the war brought both countries to the brink of economic disaster.

Since both countries were landlocked, imports of arms and other supplies from outside were limited to what the neighboring countries considered convenient or appropriate.

The Bolivian army was dependent on food supplies that entered southeastern Bolivia from Argentina through Yacuíba.[52] The army had great difficulty importing arms purchased at Vickers, since both Argentina and Chile were reluctant to let war material pass through their ports. The only remaining options were the port of Mollendo in Peru and Puerto Suárez on the Brazilian border.[52] Eventually Bolivia achieved partial success after Vickers managed to persuade the British government to request that Argentina and Chile ease the import restrictions imposed on Bolivia. Internationally, the neighboring countries of Peru, Chile, Brazil and Argentina tried to avoid being accused of fueling the conflict and therefore limited the imports of arms to both Bolivia and Paraguay, although Argentina supported Paraguay behind the neutrality façade. Paraguay received military supplies and daily intelligence from Argentina, which also provided Paraguay with critical economic and military backing throughout the war.[1][2]

The Argentine army established a special detachment along the border with Bolivia and Paraguay at Formosa in September 1932, called Destacamento Mixto Formosa, in order to deal with deserters from both sides trying to cross into Argentine territory and to prevent any boundary crossing by the warring armies,[53] although the cross-border exchange with the Bolivian army was banned only in early 1934, after a formal protest by the Paraguayan government.[54] By the end of the war 15,000 Bolivian soldiers had deserted to Argentina.[55] Some native tribes living on the Argentine bank of the Pilcomayo, like the Wichí and Toba people, were often fired at from the other side of the frontier or strafed by Bolivian aircraft,[56] while a number of members of the Maká tribe from Paraguay, led by deserters who had looted a farm on the border and killed some of its inhabitants, were engaged by Argentine forces in 1933.[57] The Maká had been trained and armed by the Paraguayans for reconnaissance missions.[58] After the defeat of the Bolivian army at Campo Vía, at least one former Bolivian border outpost, Fortin Sorpresa Viejo, was occupied by Argentine troops in December 1933. This led to a minor incident with Paraguayan forces.[59][60]

A number of volunteers and hired personnel from different countries participated in the war on both sides. The high command staff of both countries was at times dominated by Europeans. In Bolivia, Gen. Hans Kundt, a German First World WarEastern Front veteran, was in command from the beginning of the war until December 1933, when he was relieved due to a series of military setbacks. Apart from Kundt, Bolivia had also been advised in the last years of the war from a Czech military mission made of First World War veterans.[61] Paraguay was getting input from two White Russian generals, Ern and Belaieff; the latter was part of Gen. Pyotr Wrangel's staff during the Russian Civil War. In the later phase of the war Paraguay would receive training from a large-scale Italian mission.[62]

Bolivia had more than 107 Chileans fighting on its side. Three died from different causes in the last year of the conflict. The Chileans involved in the war enrolled privately and were mostly military and police officers. They were partly motivated by the unemployment caused by both the Great Depression and the political turbulence in Chile in the early 1930s (some of the Chilean officers went after the Chaco War ended to fight in the International Brigades during the Spanish Civil War).[63] The arrival of the first group of Chilean combatants to La Paz sparked protests from Paraguay and led the Chilean Congress on 7 September 1934 to approve a law that made it illegal to join the armies of countries at war.[63] This did not, however, stop the enrollment of Chileans in the Bolivian army, and it has been argued that Chilean President Arturo Alessandri Palma secretly approved of the practice in order to get rid of potentially troublesome elements of the military.[63]

The enrollment of Chilean military personnel in the Bolivian army caused surprise in Paraguay, since former Chilean president Gen. Carlos Ibáñez del Campo in 1928 had supported Paraguay after the Bolivian reprisals for the destruction of Fortin Vanguardia. The Paraguayan press denounced the Chilean government as not being neutral and went on to claim that the Chilean soldiers were mercenaries.[63] On 12 August 1934 the Chilean ambassador in Asunción was recalled back to Santiago in response to official Paraguayan support of the accusations against the Chilean government in the press. Early in the war, however, a few Chilean officers had joined the Paraguayan army.[63]

At least two Uruguayan military pilots, Benito Sánchez Leyton and Luis Tuya, volunteered for some of the most daring missions carried out by Paraguayan Air Force Potez 25s, like the resupply of besieged forces during the Battle of Cañada Strongest and the mass air strike on the Bolivian stronghold of Ballivián on 8 July 1934. During the relief mission on Cañada Strongest, Leyton's Potez nº 7 managed to come back home despite having been hit by almost 200 rounds.[64]

Argentina was a source of arms and ammunition for Paraguay. The Argentine military attaché in Asuncion, Col. Schweizer, continued to advise the Paraguayan command well after the start of hostilities. However, the more valuable contribution to the Paraguayan cause came from Argentine military intelligence (G2), led by Col. Esteban Vacareyza, which provided nightly reports on Bolivian movements and supply lines running along the border with Argentina.[65] Argentine First World War veteran pilot Vicente Almandoz Almonacid was appointed Director of Military Aviation from 1932 to 1933.[66]

The open Argentine support for Paraguay was also reflected on the battlefield when a number of Argentine citizens, largely from Corrientes and Entre Ríos, volunteered for the Paraguayan army.[67] Most of them served in the 7th Cavalry Regiment "General San Martín" as infantrymen. They fought against the Bolivian Regiments "Ingavi" and "Warnes" at the outpost of Corrales on 1 January 1933, where they had a narrow escape after being outnumbered by the Bolivians. The commander of the "Warnes" Regiment, Lt. Col. Sánchez, was killed in an ambush set up by the retreating forces, while the volunteers lost seven trucks.[68] The greatest achievement of "San Martín" took place on 10 December 1933, when the First Squadron, led by 2nd Lt. Javier Gustavo Schreiber, ambushed and captured the two surviving Bolivian Vickers six-ton tanks on the Alihuatá-Savedra road, in the course of the battle of Campo Vía.[69]

By the time a ceasefire was negotiated for noon June 10, 1935, Paraguay controlled most of the region. In the last half-hour there was a senseless shootout between the armies. This was recognized in a 1938 truce, signed in Buenos Aires in Argentina and approved in a referendum in Paraguay, by which Paraguay was awarded three-quarters of the Chaco Boreal, 20,000 square miles (52,000 km2). Two Paraguayans and three Bolivians died for every square mile. Bolivia did get the remaining territory that bordered Puerto Busch.

Over the succeeding 77 years, no commercial amounts of oil or gas were discovered in the portion of the Chaco awarded to Paraguay, until 26 November 2012, when Paraguayan President Federico Franco announced the discovery of oil reserves in the area of the Pirity river. According to Franco these oilfields will make Paraguay an oil-producing nation by mid-2013.[70] The President claimed that "in the name of the 30,000 Paraguayans who died in the war" the Chaco will become the richest oil-bearing region in South America.[71] Oil and gas resources extend also from the Villa Montes area and the portion of the Chaco awarded to Bolivia northward along the foothills of the Andes. Today these fields give Bolivia the second largest resources of natural gas in South America after Venezuela.[72]

Paraguay captured 21,000 Bolivian soldiers and 10,000 civilians (1% of the Bolivian population); many chose to stay in Paraguay after the war.[citation needed] In addition, 10,000 Bolivian troops—many of them ill-trained and ill-equipped conscripts—deserted to Argentina or injured or mutilated themselves to avoid combat.[citation needed] Paraguay also captured 2,300 machine guns, 28,000 rifles and ammunition worth $10 million (enough to last 40 years).[citation needed]

Bolivia's stunning military blunders during the Chaco War led to a mass movement known as the Generación del Chaco, away from the traditional order,[73] which was epitomised by the MNR-led Revolution of 1952.

A final treaty clearly marking the boundaries between the two countries was not signed until April 28, 2009, in Buenos Aires.[74]

Augusto Céspedes, the Bolivian ambassador to UNESCO, and one of the most important Bolivian writers of the 20th century, has written several books describing different aspects of the conflict. As a war reporter for the newspaper El Universal Céspedes had witnessed the penuries of the war, which he described in Crónicas heroicas de una guerra estúpida ("Heroic Chronicles of a stupid war") among other books. Several of his fiction works, considered masterworks of the genre, have also the Chaco War conflict as setting. Another diplomat and important figure of Bolivian literature, Adolfo Costa du Rels, has written about the conflict, his novel Laguna H3 published in 1938 is also set in the Chaco War.

One of the masterpieces of Paraguayan writer Augusto Roa Bastos, the 1960 novel Hijo de Hombre, describes in one of its chapters the carnage and harsh war conditions during the siege of Boquerón. The author himself took part in the conflict, joining the army medical service at the age of 17. The Argentine film Hijo de Hombre, directed by Lucas Demare in 1961 is based on this part of the novel.

In Pablo Neruda's poem, Standard Oil Company, Neruda refers to the Chaco War in the context of the influences that oil companies had on the existence of the war.[75]

^"Paraguayan victory in the Chaco War doubled the national territory and worked wonders for national pride." Chasteen, John Charles (2001). Born in Blood and Fire: A Concise History of Latin America. Norton, p. 176. ISBN 978-0-393-05048-6

^"The architect of the Paraguayan victory was General Estigarribia, who fought a brilliant war of maneuver." Goldstein, Erik (1992). Wars and peace treaties, 1816–1991. Routledge, p.185. ISBN 978-0-415-07822-1

^English, Adrian J. "The Green Hell: A Concise History of the Chaco War Between Bolivia and Paraguay 1932–1935." Gloucestershire: Spellmount Limited, 2007.